What's the Best Cardio? (It Depends on Your Goals)

Bottom line: Your body has three energy systems. Each one responds to different training and uses different fuel. Match your cardio to your actual goal.

Energy SystemHeart RateDurationFuel SourceBest ForCreatine Phosphate85-95%0-12 secCreatine phosphateStrength, power, leaning outGlycolytic75-85%10-90 secCarbsBuilding muscle, hypertrophyOxidative65-75%90+ secFatWeight loss, endurance

I'm gonna be going over the different energy systems in the body. This matters when you're setting your exercise routine. We want to make sure what you're doing is relevant to what your goals are.

If your goal is to lose weight, you don't want to be doing an exercise routine that is more ideal for someone looking to build muscle. That's not your goal. The energy systems in your body dictate that.

The three energy systems

We have three different energy systems: the creatine phosphate system, the glycolytic system, and the oxidative system.

Let me put this into more regular English.

System 1: Creatine phosphate (strength)

Heart rate around 85 to 95 percent. High intensity work, up to about 10 to 12 seconds. Not a very long time at all.

Think of athletic events: a hundred meter dash, a pitcher throwing a pitch. In the weight room, a 1 rep max or a set of two or three.

This energy system encourages your body to become stronger. If you're looking to increase your 1 rep max on bench, or just looking to be stronger overall, this is the system to train.

If you want cardio that supports this, do high intensity intervals. Work for 10 seconds at 100 percent effort, rest for up to a minute, repeat. Plyometrics work well here too.

System 2: Glycolytic (muscle building)

Heart rate at 75-85 percent. Work lasting 10 to 90 seconds. Weightlifting in that 6 to 12 rep range.

The main fuel source here is carbs.

This matters because there's a lot of diets out there saying carbs are the enemy. Carbs are your body's primary fuel source, especially in the glycolytic system. (ACSM guidelines on carbohydrate intake support this for athletes and active individuals.)

If you're trying a restrictive low carb diet while your goals are hypertrophy, you're working against yourself. You're looking to bulk up or increase muscle size, but you've cut off your fuel supply.

System 3: Oxidative (fat burning)

Low intensity. Heart rate at 65 to 75 percent. Work lasting 90 seconds and above.

This is your endurance runners, your joggers. From a weight room perspective, 15 to 20 reps puts you in that weight loss, fat burning range.

The primary fuel source here is fat.

If your main goal is weight loss, this is where you want to live. Low intensity steady-state cardio is your friend. Hop on a treadmill, elliptical, whatever you enjoy most. Go at a nice steady pace and keep it there.

Intervals are fine too, but they're not as aligned with fat loss as staying in this oxidative system.

Match your training to your goals

When you're setting an exercise plan and goals for yourself, have both aesthetic goals and performance goals. That way you don't get too caught up on one or the other.

But make sure your cardio matches what you're actually trying to accomplish. Don't just default to whatever you've always done.

Further reading:

• ACSM Guidelines on Exercise Intensity
• NSCA on Energy System Development